The application with follwing web.xml can not be deployed.
---
<servlet>
<servlet-name>sample</servlet-name>
<servlet-class>sample.TheServlet</servlet-class>
<security-role-ref>
<role-name>users</role-name>
</security-role-ref>
</servlet>
<servlet-mapping>
....
</servlet-mapping>
<security-role>
<role-name>users</role-name>
</security-role>
---
"java.lang.IllegalArgumentException: Can't convert argument: null" occurred.
The Specification says:
---
The security-role-ref element declares the security role reference in a
component’s or in a deployment component’s code.
It consists of an optional description, the security role name
used in the code(role-name), and an optional link to a security role(role-link).
---
<role-link> is optional.

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